unset会话变量那些以cart开头

i have a session variables with name

$_session['cart_10'], $_session['cart_2'], $_session['cart_8'], $_session['cart_110'], $_session['city'], $_session['location'], $_session['store_id']

now i want to unset all session variable that start with 'cart' like following session variable

$_session['cart_10'], $_session['cart_2'], $_session['cart_8'], $_session['cart_110']

please help me to solve that problem

Checkout this function

function unsetcart($a)
{
    foreach($_SESSION as $k => $v)
    {
        if(substr($k, 0, strlen($a))==$a)
        {
            unset($_SESSION[$k]);
        }
    }
    return 1;
}

unsetcart('cart_');